JP2009294652A - Optical element for led - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress color unevenness in a radiation surface and illumination unevenness while suppressing the reduction of a front light quantity of light emitted from a plurality of LEDs to the minimum and to reduce the glare in an emission surface. <P>SOLUTION: In a light source including the plurality of LEDs discretely disposed and an optical element for LEDs disposed on the front side in a radiation direction of the light source, the optical element for the LEDs is formed by using a light scattering light guide body to which volumetrically uniform scattering ability is given. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical element for LED.

In a lighting device using an LED as a light source, white light is obtained by combining white light using a combination of a blue LED chip and a yellow phosphor (see, for example, Patent Document 1), or using RGB LED chips. The method of obtaining is common. However, when the blue LED chip and the yellow phosphor are combined, there is a color temperature distribution between the light near the center of the blue LED chip and the light around it, and as a result, the light near the center on the irradiated surface. Ambient light is yellowish compared to. This is called a so-called yellow ring. On the other hand, in the method of obtaining white light by combining the red LED chip, the green LED chip, and the blue LED chip, when one of the LED chips is aligned with the optical axis, the remaining two chips are light. It will be displaced from the axis. Alternatively, even if the optical axes are installed at the positions of the centers of gravity of the three chips, the respective chips are also arranged so as to be shifted from the optical axis of the lens. As a result, the irradiation areas of red, green, and blue are shifted on the irradiation surface and mixed unevenly. Moreover, in the LED chip that uses a plurality of LED chips arranged side by side in order to obtain higher luminance, there may be a case where the illumination surface has uneven illuminance due to the fact that the light source is shifted from the optical axis. .
Furthermore, in general wire bonding of electrodes, the wire may become a shadow and affect the irradiated light. As a countermeasure against these problems, a technique for preventing color unevenness, light and darkness, etc. has been developed by arranging a diffusion sheet having an optical pattern and having a diffusion function in front of the LED chip in the irradiation direction.

JP 2008-16341 A

By the way, since the surface scattering of the diffusion sheet is basically a single scattering, if there is relatively large luminance unevenness or color unevenness, the diffusion sheet having a small diffusion angle can be diffused enough to correct the unevenness. Can not. On the contrary, in the diffusion sheet having a large diffusion angle, even if the unevenness correction can be performed, the backscattering component becomes large, and the front light amount is reduced.
Another problem is the glare of the LED light source. Since the LED has a small light emitting surface size and requires high brightness for lighting applications, there is a problem of glare of the light source. Glare is not only dazzling, but depending on the wavelength and strength, it may damage the cornea of the eye. Reduction of glare is important in lighting design, and sufficient consideration is necessary to create a comfortable lighting environment. is required.

  The problem of the present invention is that when light from a light source in which a plurality of LEDs are arranged is irradiated through at least one of a lens and a reflector, color unevenness and illuminance on the irradiation surface are suppressed while minimizing a decrease in the amount of light in front of the light. It is to suppress unevenness. Furthermore, it is to reduce glare at the exit surface.

The invention described in claim 1
A light source comprising a plurality of discretely arranged LEDs, and an LED optical element arranged in front of the light source in the irradiation direction, by a light scattering light guide having a volumetric uniform scattering ability An optical element for LED, which is formed.

The invention according to claim 2 is the optical element for LED according to claim 1,
The size parameter of the light-scattering light guide, and the deviation of the center of each irradiation area of the plurality of LEDs is corrected with respect to the optical axis of the light source at a point away from the light source by a predetermined distance; It is characterized in that at least one of turbidity is set.

According to the present invention, since the LED optical element formed from the light scattering light guide is arranged in front of the irradiation direction of the light source composed of a plurality of LEDs, the light emitted from each LED is the LED optical element. The light is scattered and uniformly irradiated on the irradiated surface. Furthermore, the incident light from the small light emitting surface of the LED is diffused in the optical element and is uniformly emitted from the large light emitting surface of the optical element, so that glare can be reduced.
In addition, the scattering by the spherical particles inside the light-scattering light guide has a size parameter controlled so that light is scattered with higher directivity in the forward direction. That is, the backscattering component is suppressed, and it is possible to prevent a decrease in the front light amount.

It is a side view which shows the lens as an optical element for LED which concerns on 1st Embodiment. It is a side view which shows the shift | offset | difference of the optical axis of the said lens, and each irradiation area in case the lens of FIG. 1 is formed with the transparent PMMA lens. It is a front view which shows the shift | offset | difference with the optical axis of the lens of FIG. 2, and each irradiation area. It is a graph which shows angle distribution I ((alpha), (theta)) of the scattered light intensity by a single true spherical particle. It is a side view which shows the lens as an optical element for LED which concerns on 2nd Embodiment. It is a graph which shows the relationship between relative intensity | strength when the spherical particle contained in the light-scattering light guide which makes the lens of FIG. 5 is 2 micrometers, and an angle.

[First Embodiment]
FIG. 1 is an explanatory view showing a lens as an optical element for LED according to the present invention. A lens 1 shown in FIG. 1 is a biconvex lens, and is disposed in front of an irradiation direction of a light source 10 composed of a plurality of LEDs (first LED 11, second LED 12, and third LED 13) discretely disposed on a plane. Yes. The positional relationship between the lens 1 and the light source 10 is a positional relationship in which the light source 10 is disposed at the focal length of the lens 1.
The first LED 11, the second LED 12, and the third LED 13 are arranged at equal intervals along a direction orthogonal to the optical axis 2 of the lens 1. The central second LED 12 is arranged on the optical axis 2.

  Here, in the case where the lens 1 is formed of a transparent PMMA lens, the center position b1 of the irradiation area B1 of the second LED 12 on the irradiation surface separated from the light source 10 by a predetermined distance as shown in FIGS. Is substantially the same as the optical axis 2, but the center position a1 of the irradiation area A1 of the first LED 11 is shifted from the optical axis 2 by A, and the center position c1 of the irradiation area C1 of the third LED 13 is also only from the optical axis 2 to C. It will shift.

  On the other hand, when the lens 1 is formed of a HSOT (High Scattering Optical Transmission) polymer as a light scattering light guide according to the present invention, the light incident on the lens 1 as shown in FIG. And is scattered with a certain spread angle from the exit surface. The spread angle is determined by the center position a1 of the irradiation area A1 of the first LED 11 and the second LED 12 on the irradiation surface separated from the light source 10 by a predetermined distance depending on at least one of the size parameter and turbidity of the light scattering light guide. The center position b1 of the irradiation area B1 and the center position c1 of the irradiation area C1 of the third LED 13 are adjusted so as to substantially coincide with the optical axis 2.

  Hereinafter, the light scattering light guide will be described. The light scattering light guide is a light guide having a volumetric uniform scattering ability, and includes a large number of spherical particles as scattering fine particles. When light enters the lens 1, the light is scattered by the scattering fine particles.

  Here, the Mie scattering theory that gives the theoretical basis of the present invention will be described. Mie diffusion theory is the solution of Maxwell's electromagnetic equation for the case where spherical particles (scattering fine particles) having a refractive index different from that of the medium exist in a medium (matrix) having a uniform refractive index. . The intensity distribution I (α, θ) depending on the angle of the scattered light scattered by the scattering particles is expressed by the following equation (1), and the scattering efficiency K (α) is expressed by the following equation (2). α is a size parameter that is expressed by the following equation (3) and indicates the optical size of the scatterer, and corresponds to the radius r of the spherical particle (scatterer) normalized by the wavelength λ of light in the matrix. The amount to be. The angle θ is a scattering angle, and the same direction as the traveling direction of incident light is θ = 180 degrees.

Further, i1 and i2 in the formula (1) are represented by the formula (4). And a and b with subscript ν in the expressions (2) to (4) are expressed by the expression (5). P (cosθ) with superscript 1 and subscript ν is Legendre's polynomial, a and b with subscript ν are first-order and second-order Recati-Bessel functions Ψ _* , ζ _* (where “ _* ” Means the subscript ν) and its derivative. m is the relative refractive index of the scattering fine particles based on the matrix, and m = nscatter / nmattrix.

FIG. 4 is a graph showing the intensity distribution I (α, θ) by a single true spherical particle based on the above equations (1) to (5). FIG. 4 shows the angular distribution I (α, θ) of the scattered light intensity when there is a true spherical particle as a scattering fine particle at the origin and the excitation light is incident from below. The distance from the origin to each of the curves S1 to S3 is the scattered light intensity in each scattering angle direction. Curve S1 shows the scattered light intensity when α is 1.7, curve S2 shows the scattered light intensity when α is 11.5, and curve S3 shows the scattered light intensity when α is 69.2. Yes. In FIG. 4, the scattered light intensity is shown on a logarithmic scale. Therefore, although it appears as a slight difference in intensity in FIG. 4, it is actually a very large difference.
As shown in FIG. 4, the larger the size parameter α (the larger the particle size of the true spherical particle when considered at a certain wavelength λ), the more light is scattered toward the upper side (front of the irradiation direction). You can see that Actually, the angular distribution I (α, θ) of the scattered light intensity is controlled by using the radius r of the scatterer and the relative refractive index m of the medium and the scatterer as parameters if the incident light wavelength λ is fixed. can do.

  When light is incident on such a light scattering light guide containing N single spherical particles, the light is scattered by the spherical particles. Scattered light travels through the light scattering light guide and is again scattered by other spherical particles. When particles are added at a volume concentration of a certain level or more, such scattering is sequentially performed a plurality of times, and then light is emitted from the light scattering light guide. A phenomenon in which such scattered light is further scattered is called a multiple scattering phenomenon. In such multiple scattering, analysis by a ray tracing method with a transparent polymer is not easy. However, the behavior of light can be traced by the Monte Carlo method and its characteristics can be analyzed. According to this, when the incident light is non-polarized light, the cumulative distribution function F (θ) of the scattering angle is expressed by the following equation (6).

Here, I (θ) in the equation (6) is the scattering intensity of the true spherical particles having the size parameter α represented by the equation (1). Assuming that light having an intensity of I ₀ is incident on the light-scattering light guide and passes through the distance y, the intensity of the light is attenuated to I by scattering, and these relationships are expressed by the following equation (7).

Τ in the equation (7) is called turbidity and corresponds to the scattering coefficient of the medium, and is proportional to the number N of particles as in the following equation (8). In the equation (8), σ ^s is a scattering cross section.

From the equation (7), the probability P _t (L) of transmitting through the light-scattering light guide of length L without scattering is expressed by the following equation (9).

On the other hand, the probability P _s (L) scattered up to the optical path length L is expressed by the following equation (10).

  As can be seen from these equations, the degree of multiple scattering in the light scattering light guide can be controlled by changing the turbidity τ.

  By the above relational expression, it is possible to control multiple scattering in the light scattering light guide using at least one of the size parameter α and turbidity τ of the scattering fine particles as a parameter, and the outgoing light intensity and scattering angle on the outgoing surface can also be controlled. It can be set appropriately. That is, the irradiation area A1, B1, each of the optical axis 2 of the light source 10 and the plurality of LEDs (first LED 11, second LED 12, and third LED 13) at a point away from the light source 10 in FIG. If the size parameter α and the turbidity τ of the scattering fine particles are set so that the deviation from C1 is corrected, the color deviation can be canceled and made uniform.

  According to the present embodiment, the light scattering guide can control the relative refractive index of a micro non-uniform structure (particle) that does not absorb light, and attenuates light by the multiple scattering effect. And can be diffused and emitted uniformly and in a specific direction. Furthermore, since the light is averaged and emitted from the entire emission surface of the lens 1, glare can be reduced.

Of course, the present invention is not limited to the above-described embodiment and can be modified as appropriate.
For example, in this embodiment, although the lens 1 was illustrated and demonstrated as an optical element for LED which concerns on this invention, a reflector is mentioned as an optical element for LED besides this.
Further, as described above, the light from the light source 10 may be transmitted through a plurality of optical elements without passing through only one optical element.

[Second Embodiment]
In the first embodiment, the case where the LED optical element is a biconvex lens (lens 1) has been described as an example. However, in the second embodiment, the case where the LED optical element is a single convex lens is illustrated. To explain.

  FIG. 5 is a side view showing a lens as an optical element for LED according to the second embodiment. As shown in FIG. 5, the lens 20 is a single convex lens, and is arranged in front of the irradiation direction of the light source 30 composed of a plurality of LEDs (first LED 31 and second LED 32) discretely arranged on a plane. . On the convex surface of the lens 20, a notch 21 in which the first LED 31 and the second LED 32 are accommodated is formed. The first LED 31 and the second LED 32 are arranged at equal intervals along the optical axis 22 along the direction orthogonal to the optical axis 22 of the lens 20.

  The light scattering light guide forming the lens 20 is made of, for example, a polytyl methacrylate resin. This polytyl methacrylate resin contains a large number of spherical and translucent silicone particles having a particle diameter of 1 to 10 μm as scattering fine particles.

Here, it is assumed that the optical axis distance H between the first LED 31 and the second LED 32 is 1.5 mm, and the thickness T from the notch 21 to the exit surface 23 of the lens 20 is 12 mm. When the diameter of the scattering fine particles of the lens 2 is 2 μm, the single scattering half-value angle θ of the scattering fine particles is an angle (6.1 °) when the relative intensity in the graph of FIG. 6 is 0.5. .
Moreover, the average distance (free path) from one scattering to the next is expressed by the reciprocal (1 / τ) of turbidity τ. The number of scattering times N inside the lens having the thickness T is expressed by N = τ · T. The number of scattering times N is preferably 0.1 or more and 50 or less. For example, when N = 2, the scattering half-value angle θ of the entire lens is 8.6 ° as shown in the following formula (11).

  Since the spreading distance H1 of the light beam on the exit surface 23 of the lens 20 is expressed by H1 = 2T · tan θ, H1 = 3.63 mm when the value obtained as described above is substituted. That is, since the light beam spreading distance H1 on the exit surface 23 is about 2.5 times the optical axis distance H between the first LED 31 and the second LED 32, the light beam from the first LED 31 and the second LED 32 The light beams overlap with each other, and the light beams are emitted uniformly from the light exit surface 23, and unevenness is corrected.

1 Lens (LED optical element)
2 Optical axis 10 Light source 11 First LED
12 Second LED
13 Third LED
20 Lens (LED optical element)
22 Optical axis 30 Light source 31 First LED
32 Second LED

Claims (2)

  A light source comprising a plurality of discretely arranged LEDs, and an LED optical element arranged in front of the light source in the irradiation direction, by a light scattering light guide having a volumetric uniform scattering ability An optical element for LED, which is formed. The optical element for LED according to claim 1,
The size parameter of the light-scattering light guide, and the deviation of the center of each irradiation area of the plurality of LEDs is corrected with respect to the optical axis of the light source at a point away from the light source by a predetermined distance; At least one of turbidity is set, The LED optical element characterized by the above-mentioned.

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